Known apparatuses for resistance welding comprise two opposite electrodes that are supported by electrode supporters, in such a way that the electrodes may be moved toward one another. The electrodes are used, at the same time, as components of the circuit to which power is supplied to the electrodes during the welding process; workpieces to be welded, are to be placed between the electrodes, for the performance of the welding process, and contact is established between the electrodes and the workpieces. After applying power and/or after the welding current has started flowing, current flows through the workpieces to be welded and, due to the relatively high resistance, heat is generated that melts the surfaces of the workpieces to be welded and welds them together. During that welding process, a reduction of the dimensions of the workpieces, as measured in the axial direction of the electrodes takes place; this reduction needs to be compensated for in some way, such as, following up with at least one electrode, in order to maintain contact between the electrodes and the workpieces. For that reason, the electrodes may be pre-stressed, in relation to one another, by means of an elastic member, such as a spring. The force of the elastic member provides the "electrode power" to ensure a sufficiently secure position of the workpieces to be welded before welding, as well as, the follow-up of the electrodes during the welding process and the constant contact of electrodes and workpieces.
When workpieces of highly conductive materials, e.g. of little contact plates of pure silver, are welded, it is necessary that the transfer resistance at the location of weld at the beginning of the welding process be maximal, for the performance of a resistance weld. For that reason, the small pure-silver contact plates are designed with pointed mounting, so that they are in contact with the workpiece to which they are to be welded, e.g. to a contact supporter, by way of point contact or line contact, but not by way of surface contact. It is necessary to choose an electrode power that is sufficiently small so that the points of the mounting will not be damaged or penetrate the contact mounting. But, an electrode power which is that small, does not ensure an optimal follow-up of the electrodes.
The electrode supporters usually comprise two generally linear parallel rail connectors each of which supports one of the electrodes on one end is connected with a connection cable on the other end. The rail connectors are mounted in such a way that they may be moved in relation to one another, so that the electrodes held on the rail connectors may be moved toward one another. When a current is applied, the current flows through the rail connectors in opposite directions. The magnetic field that appears in conductors through which the current flows in such anti-parallel directions, generates an electro-magnetic force which moves the rail connectors apart. The electro-magnetic force counteracts or acts against the electrode power, so that the pre-stress of the electrodes in relation to the workpieces to be welded will be reduced when workpieces of highly conductive material are welded, a high current intensity is required to weld them if they are touching by point contact. Due to the high current intensity which, when small pure-silver contact plates are welded, may amount to several thousands of amps, the electro-magnetic force that acts between the rail connectors, increases considerably, so that the electrode power that is generated by the elastic member, will be largely compensated. It is even possible that the electro-magnetic force causes a lift-off of the electrodes from the workpieces to be welded; that makes welding of those workpieces impossible. It is not possible to increase the pre-stress of the electrodes because it may damage the mounting points or push them into the contact supporter. The point contact between, e.g. the small pure-silver contact plates and the contact mounting would, in that case, not exist any longer. Due to the surface contact which would prevail in that case between the components of highly conductive materials to be welded, the formation of a correct welded joint would not be possible.
The invention is based on the problem of creating a device for resistance welding that makes it possible also to weld pressure-sensitive parts or workpieces, and that ensures a sufficient follow-up of electrodes as well as their constant lying against or contact with the workpieces to be welded.